A Multi-Protocol Label Switched (MPLS) network is a communication network made up of a plurality of network devices which transfer or forward packets of information using so-called virtual connections referred to as “label switched paths” (LSPs).
A conventional LSP begins at a source network device, passes through intermediate network devices and ends at a destination network device.
If a failure at a network device or link (failure point) occurs downstream of a source network device, so-called existing MPLS Fast Re-routing techniques are employed to bypass the failure.
Existing MPLS Fast Re-routing techniques are effective in re-routing MPLS labeled traffic in an LSP acting independently relative to other LSPs. However, when LSPs are bundled together to operate in two directions, such as in bi-directional LSPs disclosed in U.S. patent application Ser. No. 10/613,104, MPLS Fast Re-routing does not perform well.
MPLS Fast-Re-routing attempts to re-route traffic from a forward LSP to a predetermined alternate path. However, because many times there is no predetermined alternate path for a backward LSP in a bi-directional LSP, once a failure occurs no traffic is allowed to flow in the backward direction. As a result, the bi-directional LSP can no longer operate as a bi-directional LSP; it now operates as a uni-directional LSP.
MPLS Fast-Re-routing is also deficient when both the forward and backward LSPs do in fact have alternate LSPs. In such a instance, MPLS Fast-Re-routing creates two separate alternate paths (i.e., using different network elements) one for each direction, to overcome a failure. One path allows traffic in an original, forward LSP to bypass a failure while the other path allows traffic from an original backward LSP to bypass the failure. Creating different alternate paths for the forward and backward LSPs of a bi-directional LSP makes it difficult to ensure the same quality of service.